Clamp mechanism

ABSTRACT

A clamp mechanism for selectively locking and unlocking a first member in a first position relative to a second member comprises a linkage system connecting the first and second members and drive means for articulating the linkage system for moving the first member relative to the second member. A fluid link is provided for locking the first member in position relative to the second member wherein the fluid link is actuated upon sensing the first member approaching the first position.

BACKGROUND OF THE INVENTION

The present invention relates to an improved clamp mechanism and methodfor operating same and, more particularly, an improved clamp mechanismfor use in a reciprocating press such as an injection molding machinewherein a fluid link is employed to affect the clamping of a pair ofplaten halves together.

Toggle clamps used in presses for injection molding, compressionmolding, die casting and the like are well-known in the art. A typicaltoggle clamp mechanism is disclosed in U.S. Pat. No. 3,117,348 to Reesand Schad which is assigned to the assignee of the present invention. Asdisclosed in U.S. Pat. No. 3,117,348, the toggle mechanism is actuatedby a connecting rod which works in conjunction with a rotating diskwhich is driven by a variable speed drive motor. The mechanism isdesigned so as to allow for the disk to rotate always in the samedirection. In order to actuate the toggle mechanism a pinion gearprovided on the disk engages the drive shaft of the variable speed motorby means of a clutch. The disk rotates so as to push and pull the togglesystem which is articulated by the connecting rod which links therotating disk with the center pin of the toggle system. When the togglesystem is stretched out the platens of the press abut each other and arein their locked position. In the stretched out position, the pinion isunclutched from the drive motor and a brake is applied so that theconnecting rod and the corresponding toggle mechanism, which are now intheir stretched out position, are immobilized so as to lock the platensin place. The locking force is transmitted linearly from the spacebetween the platens onto the abutment holding the toggle system and anymovement of the center link of the toggle system, which would result inthe release of the clamping action, is absorbed by the fixed position ofthe disk pinion and connecting rod thereby resulting in the entireassembly being immobilized. As can be seen from the foregoing theopening and closing movements of the platens is effected by the rotatingdisk via the connecting rod and linkage system whereby the connectingrod holds and pushes the toggle links corresponding to the opened andclosed positions of the patens. The rotating disk is stopped by theclutch and brake arrangement in one or both of the positionscorresponding to the fully opened and fully locked positions of theplatens.

The primary advantages of the toggle system as described above is itsgreat speed, that is, the opening and closing sequence of the platens iscarried out without the necessity of reversing the actuating element asis customarily required by other known toggle systems which aretypically actuated by reciprocating cylinders. While the above-describedsystem has been used extensively in industry it nevertheless has certaindrawbacks and disadvantages when employed in systems requiring lockingforces in excess of 250 tons. In particular, it has been found that thetransmission system tends to be overstressed and therefore not functionwith the desired degree of reliability when attempts are made toincrease the locking force that may be exerted by the system. Inaddition, the drive provided by a motor with a conventional variablespeed pulley drive tends to be oversized and the drive itself notadequate for the operation of large clamps thereby requiring the use ofalternate mechanicam drives which tend to be large, occupy a great dealof space in a given machine and quite expensive. Finally, the clutch andbrake system employed is not designed for highly stressed conditions. Tosummarize, when working with locking forces in excess of 250 tons thereliability of the system described above is limited.

Naturally it would be highly desirable to provide a clamp mechanismsuitable for use in reciprocating presses and the like which overcomethe problems noted above with regard to prior art clamp mechanisms.

Accordingly, it is the principal object of the present invention toprovide a novel transmission suitable inter alia for use with clampmechanisms for selectively locking and unlocking a member in place.

It is a particular object of the present invention to provide a clampmechanism as aforesaid which is particularly useful in reciprocatingpresses such as pressure molding machines.

It is a further object of the present invention to provide atransmission as aforesaid which employs a fluid link for positioning amember in place.

It is a still further object of the present invention to provide aclamping mechanism as aforesaid in a reciprocating press wherein meansare provided for sensing an obstruction between the relatively movablepress members.

It is another still further object of the present invention to provide aclamp mechanism as aforesaid which is of simple construction, economicto manufacture and easily used with a high degree of reliability.

Further objects and advantages of the present invention will appearhereinbelow.

SUMMARY OF THE INVENTION

In accordance with the present invention, the foregoing objects andadvantages are readily obtained.

The present invention relates to an improved transmission for operatingsame and, more particularly, an improved clamp mechanism incorporatingsuch transmission for use in a reciprocating press wherein a fluid linkis employed to effect the clamping of a pair of platen halves together.The device of the present invention comprises a first movable memberconnected by a linkage system to a second stationary member. The linkagesystem is articulated by means of a drive for moving the first memberrelative to the second member. A locking mechanism is associated withthe linkage system for locking the first member in place relative to thesecond member at a predetermined distance from said second member. Inaccordance with the principal feature of the present invention, asensing element is provided for sensing when the first member isproximate to the predetermined distance from the second member foractivating the fluid link for locking the first member in place. Thesensing means may take the form of a conventional limit switch which isactivated by the drive mechanism. In accordance with the presentinvention, the fluid link comprises a cylinder having a pistonreciprocally mounted therein for dividing the cylinder into first andsecond chambers wherein fluid under pressure is fed to and from thefirst and second chambers upon the sensing of the location of the firstmember by the sensing mechanism so as to lock the first member in place.

When employing the clamp mechanism of the present invention in areciprocating press wherein a movable platen is reciprocated relative toa fixed platen between a first position wherein the platens abut and asecond position wherein the platens are fully opened, a sensingmechanism is provided for sensing an obstruction between the fixedplaten and the movable platen for inactivating the fluid link so as toprohibit damage to the platen halves. The term "platens" as used hereindenotes the platens together with components such as mold elements thatmay be attached thereto.

The device of the present invention offers significant advantages overclamp transmission mechanisms and methods used heretofore. First, byproviding a fluid link for locking the toggle mechanism in place,locking forces in excess of 250 tons can be effected without stressingthe clamp actuating mechanism excessively. In addition, the clampmechanism of the present invention assures a high degree of reliabilityheretofore not obtainable by prior art devices.

Further advantages of the present invention will appear hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of the clamp mechanims in accordancewith the principles of the present invention.

FIG. 2 is a side view of the mechanism of FIG. 1.

FIG. 3 is a schematic illustration of a second embodiment of the clampmechanism in accordance with the principles of the present invention.

FIG. 4 is a schematic illustration of a third embodiment of the clampmechanism in accordance with the principles of the present invention.

DETAILED DESCRIPTION

While the present invention will be described with reference to areciprocating press and in particular a reciprocating press clamp forpressure molding, it should be appreciated that the transmissionmechanism of the present invention may be employed in many otherenvironments without departing from the scope of the instant invention.

Referring to the drawings, and particularly FIGS. 1 and 2, areciprocating press 10 is illustrated showing the clamp mechanism of thepresent invention. The press 10 comprises an abutment 12 and a fixedplaten 14 mounted on supports 16 in spaced apart relationship. Thesupports 16 are in the form of tie bars. A movable platen 18 is mountedon the tie bars 16 between the abutment 12 and the fixed platen 14 andis capable of reciprocal movement on the tie bars 16 in the directionshown by the arrow by means of linkage system 20.

The linkage system 20 comprises a first link 22 having one end 24rotatably mounted to the abutment member 12 and its other end 26rotatably mounted to a link pin 28 and a second link member 30 havingone end 32 rotatably mounted to movable platen 18 and the other end 34rotatably mounted to the link pin 28 such that the first link 22 and thesecond link 30 are joined by the link pin 28.

In accordance with a particular feature of the present invention, thelinkage system 20 as shown in the embodiment of FIG. 1 is connected todrive disk 36 by means of a connecting rod in the form of a lengthvarying fluid link 40. As shown in FIG. 1 the fluid link comprises acylinder 42 having a piston 44 reciprocally mounted therein for dividingthe cylinder into first and secnd chambers 46 and 48, respectively. Thepiston 44 is provided with a piston rod 50 which is pivotably secured tolink pin 28 of linkage assembly 20. The cylinder 42 is provided with anarm 52 for rotatably mounting the cylinder 42 on the drive disk 36 in aneccentric manner. Naturally, it should be appreciated that an equivalentstructure can be obtained by reversing the fluid link, that is, byconnecting the cylinder 42 to the link pin 28 and the piston 44 to thedrive disk 36 via piston rod 50. Fluid lines 54 and 56 are connected tochambers 46 and 48, respectively, for communicating fluid under pressurefrom a source 58 selectively via valves 60 and 62 to and from thechambers 46 and 48 in a manner to be discussed in detail hereinbelow.

Drive disk 36 is rotatably secured to the output shaft 64 of a hydraulicmotor 66. The rotational speed of shaft 64 of hydraulic motor 66 iscontrolled by feeding fluid under pressure to the hydraulic motor in amanner that is well-known in the art. The drive disk 36 is provided witha cam 68 mounted on the periphery thereof which is adapted to operatelimit switch 70 in a manner to be made clear hereinbelow.

The operation of the clamp mechanism of the present invention is asfollows. Fluid motor 66 drives disk 36 thereby causing the linkagesystem 20 to move movable platen 18 under the action of the fluid link40. As the disk 36 rotates and platen 18 is moved toward fixed platen 14the toggle links 22 and 30 begin to stretch out and approach an alignedposition. When the links are aligned the platens 14 and 18 are lockedtogether. Just before that position is reached, that is, the links arealigned, the rotation of the drive disk 36 is such that cam 68 tripslimit switch 70. The tripping of limit switch 70 by cam 68 results influid under pressure from source 58 to be fed via valve 62 and line 56to chamber 48 for aligning the links 22 and 30 thereby clamping andlocking the platens 14 and 18 together. At the same time the limitswitch causes the drive disk 36 to be stopped. This may be accomplishedin any known manner such as by unclutching the drive disk 36 from motor66 and applying a brake to the drive disk or, preferably, byinterrupting the flow of supply fluid to motor 66. To unlock the linkagesystem, valves 60 and 62 are moved so as to drain fluid from chamber 48via line 56 and deliver fluid under pressure to chamber 46 via line 54.The increase in pressure in chamber 46 pushes the links out ofalignment. The drive disk 36 is again caused to rotate, as by the fluidmotor 66, in the same direction as before continuing the movement of thelinks 22 and 30 so as to move the platen 18 away from fixed platen 14.

As can be seen from the foregoing description the drive mechanism, thatis, the drive disk 36, hydraulic motor 66 and output shaft 64 are notaffected by the full thrust force that is necessary to bring the linksinto alignment for locking and holding the platen 18 in place againstfixed platen 14, but only by the force exerted axially by the fluid link40. Instead, the full thrust force is taken up solely by the link pin28, the links 22 and 30 and pins 24 and 32, all of which are readilydesigned to cope with the forces exerted during locking. In order tounlock the clamp mechanism a higher force is usually required than thatto bring the clamp mechanism into locking position. For this reason, itis preferable to use the larger surface area of the piston 44 in chamber46 to unlock the clamp mechanism. However, it should be appreciated, theopposite arrangement as previously discussed is feasible. As notedabove, the control of the fluid link is affected by actuation of thehydraulic valves directly by means of cam 68 on drive disk 36 whichactivates limit switch 70. In addition, as previously noted the fluidmotor 66 and output shift 64 may advantageously be connected to drivedisk 36 by a clutch in a manner similar to that shown in prior art U.S.Pat. No. 3,117,348 discussed above. In such an arrangement the fluidmotor 66 may run uninterrupted and the final stop and start movement ofdrive disk 36 may be affected by a brake without the need of slowing themotor.

In accordance with a further feature of the present invention, thereciprocating press is provided with a safety feature for detecting anobstruction between the platens 14 and 18 for inactivating the fluidlink upon sensing such an obstruction.

A limit switch 72 is provided on the fixed platen 14 and is activated bymovable platen 18 when the movable platen 18 is sufficiently close tofixed platen 14 so as to have the platens touch. A pressure transducer74 is provided for sensing an increase in fluid pressure in chamber 48for reasons to be expanded on in detail hereinbelow. Alternatively, aconventional linear transducer could be substituted for the pressuretransducer 74 for sensing a change in length of the fluid link 40 ormovement of the piston 44.

The operation of the safety feature is as follows. Fluid pressure iscontinuously fed to chamber 48 during the rotation of drive disk 36 soas to maintain piston 44 in a position corresponding to the minimumlength of the fluid link. Assuming that an obstructing object is leftbetween fixed platen 14 and platen 18, as the platen 18 moves towardfixed platen 14 the obstruction tends to stop the motion of the platen18 even though drive disk 36 causes the length of the fluid link toincrease, that is, the piston 44 to move up in cylinder 42 therebyincreasing the pressure in chamber 48. This pressure increase in chamber48 can be sensed by pressure transducer 74. Alternatively, aconventional linear transducer may be substituted for the pressuretransducer 74 for sensing the change in length of the fluid link 40 orthe movement of piston 44 in cylinder 42. If the platens closesufficiently to cause the platens to become proximate to each other,limit switch 72 is activated to give a signal. If the first signal, thatis the signal generated by the pressure transducer or linear transducer,is detected before the second signal is generated by limit switch 72caused by the touching of the platens, then an obstruction between theplatens is thereby indicated which automatically results in thedeactivation of limit switch 70 thereby inactivating the fluid link 40.If o significant time delay occurs between the signals from pressuretransducer 74 and the signal from limit switch 72, limit switch 70 ismaintained active and upon tripping by cam 68 delivers fluid underpressure to chamber 48 so as to activate the fluid link and clamp theplatens in place.

Referring now to FIGS. 3 and 4, a second and third embodiment of theclamp mechanism of the present invention is illustrated. Contrary to theembodiment of FIGS. 1 and 2 where the fluid link 40 for locking themovable platen 18 in place comprises the connection between drive disk36 and link assembly 20, in the embodiments of FIGS. 3 and 4 theconnection between disk 36' and 36", respectively, and linkage assembly20' comprises a solid connecting rod 80. With reference to FIG. 3 thefluid link 40' for locking the movable platen .[.18'.]. .Iadd.18.Iaddend.in place adjusts the position of the drive disk 36' relative tothe abutment .[.12'.]. .Iadd.12 .Iaddend.and platen .[.14'.]..Iadd.14.Iaddend.. The drive disk 36' is rotatably supported on a baseor platform 82. The base 82 also carries the fluid motor 66 for drivingthe drive disk 36'. The base 82 is mounted for vertical movement onsupport 84 by means of guides 86. The fluid link 40' of the presentinvention is provided between the base 82 and the support 84 andcomprises a cylinder .[.42'.]. .Iadd.42 .Iaddend.having a piston.[.44'.]. .Iadd.44 .Iaddend.reciprocally mounted therein for dividingthe cylinder into first and second chambers .[.46'.]. .Iadd.46.Iaddend.and .[.48'.]. .Iadd.48.Iaddend., respectively, in the mannerdescribed with regard to the embodiment of FIG. 1, Piston .[.44'.]..Iadd.44 .Iaddend.is provided with a piston rod .[.50'.]. .Iadd.50.Iaddend.which is connected to the base 82. The cylinder .[.42'.]..Iadd.42 .Iaddend.is mounted directly on support 84. Naturally it shouldbe appreciated that an equivalent structure can be obtained by reversingthe fluid link, that is, by connecting the cylinder .[.42'.]. .Iadd.42.Iaddend.directly to the base 82 and the piston 44 to the support 84 viapiston rod .[.50'.]. .Iadd.50.Iaddend..

The operation of the clamp mechanism of the embodiment of FIG. 3 issimilar to that described hereinabove with reference to the embodimentof FIG. 1. Fluid .[.mtor.]. .Iadd.motor .Iaddend.66 drives disk 36'thereby causing the linkage system .[.20'.]. .Iadd.20 .Iaddend.to movemovable platen .[.18'.]. .Iadd.18 .Iaddend.under the action of the fluidlink 40'. Just before the links .[.22'.]. .Iadd.22 .Iaddend.and.[.30'.]. .Iadd.30 .Iaddend.are aligned, the rotation of drive disk 36'is such that cam .[.68'.]. .Iadd.68 .Iaddend.trips limit switch.[.70'.]. .Iadd.70 .Iaddend.thereby delivering fluid under pressure tochamber .[.48'.]. .Iadd.48 .Iaddend.in the manner described withreference to FIG. 1 for aligning the links .[.22'.]. .Iadd.22.Iaddend.and .[.30'.]. .Iadd.30 .Iaddend.thereby clamping and lockingthe platens .[.14'.]. .Iadd.14 .Iaddend.and .[.18'.]. .Iadd.18.Iaddend.together. The drive disk 36' is stopped in the same manner asdescribed above with reference to the embodiment of FIG. 1. To unlockthe linkage system the fluid is drained from chamber .[.48'.]. .Iadd.48.Iaddend.and fluid pressure is delivered to chamber .[.46'.]. .Iadd.46.Iaddend.thereby pushing the links out of alignment. The drive disk 36'is again driven by the fluid motor 66 and rotates in the .[.sme.]..Iadd.same .Iaddend.direction as before continuing the movement of links.[.22'.]. .Iadd.22 .Iaddend.and .[.30'.]. .Iadd.30 .Iaddend.so as tomove the platen .[.18'.]. .Iadd.18 .Iaddend.away from platen .[.14'.]..Iadd.14.Iaddend.. In accordance with a further feature of the presentinvention, the reciprocating press employing the clamp mechanism of FIG.3 may be used in combination with the safety feature for detecting anobstruction between the platens .[.14'.]. .Iadd.14 .Iaddend.and.[.18'.]. .Iadd.18 .Iaddend.for inactivating the fluid link as waspreviously described above with reference to the embodiment of FIG. 1.

A further embodiment of the clamp mechanism of the present invention isshown in FIG. 4 wherein the base 82 is pivotably mounted to the support84. The fluid link 40" of the present invention is mounted between thebase 82 and the support 84 in the same manner as described above withregard to FIG. 3. The effect of this arrangement is the same asdescribed above with reference to FIG. 3 except that the force the fluidlink has to exert is smaller due to the leverage available through thepivoting mechanism. Thus, the piston and cylinder used in the fluid link40" of the embodiment illustration in FIG. 4 can be substantiallysmaller than that used in the embodiment of FIG. 3 and requires lessfluid under pressure thereby consuming less energy in operation. Theoperation of the fluid link 40" for clamping platen 18 in place is thesame as discussed above with reference to FIGS. 1 and 3. Again, theembodiment of the clamp mechanism of FIG. 4 may be used in combinationwith the safety feature for detecting an obstruction between the platens14 and 18 as previously discussed.

As can be seen from the foregoing, the device of the present inventionoffers great versatility and efficiency and satisfies the objects setout hereinabove. The clamp mechanism of the present invention assures ahigh degree of reliability when used with locking forces in excess of250 tons.

It is to be understood that the invention is not limited to theillustrations described and shown herein, which are deemed to be merelyillustrative of the best modes of carrying out the invention, and whichare susceptible of modification of form, size, arrangement of parts anddetails of operation. The invention rather is intended to encompass allsuch modifications which are within its spirit and scope as defined bythe claims.

What is claimed is: .[.1. A transmission assembly for moving a firstmember relative to a second member and selectively locking and unlockingsaid first member in a first position at a predetermined distance fromsaid second member comprising a linkage system connecting said firstmember and said second member, drive means for articulating said linkagesystem for moving said first member relative to said second member,connecting means for transferring motion from said drive means to saidlinkage system and locking means associated with said linkage system forlocking said first member in place relative to said second member atsaid predetermined distance, said locking means comprising a fluidlink..]. .[.2. A transmission assembly according to claim 1 wherein saidfluid link adjusts the length of said connecting means for locking saidfirst member in place..]. .[.3. A transmission assembly according toclaim 1 wherein said fluid link adjusts the position of said drive meansrelative to said first element and said second element for locking saidfirst member in place..]. .[.4. A transmission assembly according toclaim 2 wherein said fluid link forms said connecting means andcomprises a cylinder having a piston reciprocally mounted therein fordividing said cylinder into first and second chambers wherein one ofsaid piston and cylinder is connected to said linkage system and theother of said piston and cylinder is connected to said drive means..]..[.5. A transmission assembly according to claim 4 wherein valve meansare provided for selectively feeding fluid under pressure from a sourceto and from said first and second chambers..]. .[.6. A transmissionassembly according to claim 5 including means for sensing when saidfirst member is proximate to said first position at a predetermineddistance from said second member for controlling the flow of fluid underpressure to said fluid link for locking said first member in place..]..[.7. A transmission assembly according to claim 4 wherein said linkagesystem comprises a first link having one end rotatably mounted to saidfirst member and its other end rotatably mounted to a link pin and asecond link having one end rotatably mounted to said second member andits other end rotatably mounted to said link pin such that said firstlink and said second link are joined by said link pin..]. .[.8. Atransmission assembly according to claim 7 wherein said piston isprovided with a piston rod rotatably connected to said link pin and saidcylinder is rotatably connected to said drive means..]. .[.9. Atransmission assembly according to claim 8 wherein aid drive means is arotating disk and said cylinder is eccentrically mounted on saiddisk..]. .[.10. A transmission assembly according to claim 9 wherein ahydraulic motor drives said disk..]. .[.11. A transmission assemblyaccording to claim 3 wherein said fluid link comprises a cylinder havinga piston reciprocally mounted therein for dividing said cylinder intofirst and second chambers wherein one of said piston and cylinder isconnected to a base on which said drive means is mounted and the otherof said piston and cylinder is connected to a support..]. .[.12. Atransmission assembly according to claim 11 wherein valve means areprovided for selectively feeding fluid under pressure from a source toand from said first and second chambers for moving said base relative tosaid support..]. .[.13. A transmission assembly according to claim 12wherein said base is pivotably mounted..]. .[.14. A transmissionassembly according to claim 1 including means for sensing when saidfirst member is proximate to said first position at a predetermineddistance from said second member for controlling the flow of fluid underpressure to said fluid link for locking said first member in place..]..[.15. A reciprocating press comprising a support, a fixed platen and anabutment, said fixed platen and said abutment being connected on saidsupport such that said fixed platen is spaced from said abutment, amoving platen mounted on said support between said fixed platen and saidabutment, said movable platen being movable between a first positionwherein said movable platen abuts said fixed platen and a secondposition wherein said movable platen and fixed platen are apart, atransmission assembly for moving said movable platen between said firstposition and said second position, said transmission assembly comprisinga linkage system connecting said movable platen and said abutment, drivemeans for articulating said linkage system for moving said movableplaten relative to said abutment and said fixed platen, connecting meansfor transferring motion from said drive means to said linkage system andlocking means associated with said linkage system for locking saidmovable platen in place when said movable platen is in said firstposition, said locking means comprising a fluid link..]. .[.16. Areciprocating press according to claim 15 including means for sensingwhen said movable platen is proximate to said first position forcontrolling the flow of fluid under pressure to said fluid link forlocking said movable platen in said first position..].
 17. Areciprocating press according to claim .[.15.]. .Iadd.33.Iaddend.wherein said fluid link adjusts the length of said connectingmeans for locking said movable platen in said first position. . Areciprocating press according to claim .[.15.]. .Iadd.33.Iaddend.wherein said fluid link adjusts the position of said drivemeans relative to said fixed platen and said abutment for locking saidmovable platen in said first position.
 19. A reciprocating pressaccording to claim 17 wherein said fluid link .[.forms said connectingmeans and.]. comprises a cylinder having a piston reciprocally mountedtherein for dividing said cylinder into first and second chamberswherein one of said piston and cylinder is connected to said linkagesystem and the other of said piston and cylinder is connected to saiddrive means.
 20. A reciprocating press according to claim 18 whereinsaid fluid link comprises a cylinder having a piston reciprocallymounted therein for dividing said cylinder into first and secondchambers wherein one of said piston and cylinder is connected to a baseon which said drive means is mounted and the other of said piston andcylinder is connected to a support.
 21. A reciprocating press accordingto claim 19 wherein valve means are provided for selectively feedingfluid under pressure from a source to and from said first and secondchambers.
 22. A reciprocating press according to claim 19 wherein saidlinkage system comprises a first link having one end rotatably mountedto said abutment and its other end mounted to a link pin and a secondlink having one end rotatably mounted to said movable platen and itsother end rotatably mounted to said link pin such that said first linkand said second link are joined by said link pin.
 23. A reciprocatingpress according to claim 22 wherein said piston is provided with apiston rod rotatably connected to said link pin and said cylinder isrotatably connected to said drive means.
 24. A reciprocating pressaccording to claim 20 wherein said base is pivotably mounted. .[.25. Areciprocating press according to claim 15 including means for sensing anobstruction between said fixed platen and said movable platen forinactivating said locking means..]. .[.26. A reciprocating pressaccording to claim 17 including means for sensing an obstruction betweensaid fixed platen and said movable platen for inactivating said lockingmeans..].
 27. A reciprocating press according to claim .[.26.]. .Iadd.17.Iaddend.wherein said means for sensing an obstruction comprises alinear transducer which senses the change in length of said connectingmeans. .[.28. A reciprocating press according to claim 19 includingmeans for sensing an obstruction between said fixed platen and saidmovable platen for inactivating said locking means..]. A reciprocatingpress according to claim .[.28.]. .Iadd.20 .Iaddend.wherein said meansfor sensing an obstruction comprises a pressure transducer for sensingthe change in pressure in one of said first and second chambers. .[.30.A reciprocating press according to claim 20 including means for sensingan obstruction between said fixed platen and said movable platen forinactivating said locking means..]. .[.31. A reciprocating pressaccording to claim 28 wherein said means for sensing an obstructioncomprises a pressure transducer for sensing the change in pressure inone of said first and second chambers..]. .[.32. A reciprocating pressaccording to claim 16 further including means for sensing an obstructionbetween said fixed platen and said movable platen for inactivating saidlocking means..]. .Iadd.33. A reciprocating press comprising a support,a fixed platen and an abutment, said fixed platen and said abutmentbeing connected on said support such that said fixed platen is spacedfrom said abutment, a movable platen mounted on said support betweensaid fixed platen and said abutment, said movable platen being movablebetween a first position wherein said movable platen abuts said fixedplaten and a second position wherein said movable platen and fixedplaten are apart, a transmission assembly for moving said movable platenbetween said first position and said second position, said transmissionassembly comprising a linkage system connecting said movable platen andsaid abutment, drive means for articulating said linkage system formoving said movable platen relative to said abutment and said fixedplaten, connecting means for transferring motion from said drive meansto said linkage system, said connecting means including locking meansassociated with said linkage system for locking said movable platen inplace when said movable platen is in said first position, said lockingmeans comprises a fluid link and first means associated with said drivemeans for sensing when said movable platen is proximate to said firstposition for controlling the flow of fluid under pressure to said fluidlink for locking said movable platen in said first position and secondmeans associated with said fluid link for sensing an obstruction betweensaid fixed platen and said movable platen for inactivating said lockingmeans prior to said first sensing means sensing when said movable platenis proximate to said first position. .Iaddend. .Iadd.34. A reciprocatingpress according to claim 33 including third means associated with saidfixed platen for sensing when said movable platen is proximate to saidfixed platen for inactivating said second means for sensing anobstruction. .Iaddend.